There is an evolving need for Machine-to-Machine (M2M) data traffic for sundry devices provided with communication functionality, which can be addressed using mobile standards-based solutions. The ubiquity of such devices has led to the need for access to the same functionality even where conventional terrestrial mobile networks do not reach, which can be accomplished using mobile standards-based network components connected via satellite link. Doing so, however, introduces a number of unique problems that are common across many types of applications.
First, and most obvious, is the fact that it is vital to use satellite bandwidth as efficiently as possible due both to cost and, in some cases, scarcity of bandwidth. The challenge is to serve as many devices as possible in a given amount of bandwidth without overloading the network. Second, specifically in maritime environments, there are radically different legal requirements depending on where a vessel is located. When located in territorial waters (within 12 nautical miles of the territory of a country), a vessel is generally required to have a license to transmit on cellular frequencies. By contrast, when located in international waters (at least 12 nautical miles outside the territory of a country), the vessel may transmit on cellular frequencies without having a license. The different legal requirements can have a substantial impact on cellular traffic patterns as a vessel moves in and out of international waters.
As an example, a ship may transport hundreds or thousands of refrigerated containers. Each refrigerated container may be equipped with an M2M device that periodically sends status information. When the ship is in international waters, the M2M devices send the status information to a base station onboard the ship over cellular frequencies. The base station then communicates the status information to a monitoring system in the telecommunications network via a satellite link. When the ship is in territorial waters, however, such as when the ship is at port, the base station onboard the ship must stop operating in order to comply with legal requirements. In some cases, the M2M devices transmit status information to terrestrial base stations when the ship is at port. However, if the M2M devices are outside coverage of a terrestrial base station or are not allowed to access the terrestrial base station, for example, due to a lack of agreement with the owner of the terrestrial network, the M2M devices may be unable to transmit the status information. In such circumstances, the M2M devices must store a backlog of status information to be sent when cellular service becomes available. The backlog can potentially become quite large depending on factors such as the amount of time that the ship is without cellular service (which in some situations is approximately the same as the amount of time that the ship is at port), the number of M2M devices onboard the ship (which could be on the order of hundreds or thousands), and the frequency/volume of status information that the M2M devices are configured to transmit to the monitoring system.
When a ship leaves port and enters international waters, the onboard base station can resume operation. In response, all of the M2M devices onboard the ship may try to connect to the base station at roughly the same time in an effort to send their accumulated status information, which might overload the limited radio resources on the ship and limited satellite bandwidth. The resulting congestion can lead to very long delays in the delivery of the accumulated status information.
A further problem, in the case of Enhanced General Packet Radio Service (EGPRS) and similar technologies, is that the transport network does not know the priority of the data being carried over it. Thus, high priority data is just as susceptible to long delays as low priority data. For example, a critical alarm, such as the fact that a refrigerator is no longer functioning correctly and requires immediate maintenance, may be delayed while the system deals with voluminous low priority general reports/logs, such as hourly reports concerning the status of each refrigerated container (e.g., the geographical location of the container, the expected time of arrival at a destination port, or other status). Because of the potential delay in sending a critical alarm, the malfunctioning refrigerator may fail to receive the required maintenance in time to save perishable goods contained within.
Current technology also creates a problem in that when the onboard base station resumes operation, all M2M devices within the area may attempt to register. This creates what is known as a “registration storm.” During a registration storm, control channels and other system resources will be occupied as devices attempt to register, and many will fail to register due to congestion. Devices will then “back off” a (usually) random period of time and then repeat the attempt to register. This has the effect of tying up system resources, even for registration attempts that are doomed to fail, that could otherwise have been used for transferring high priority data.